1. Field of the Invention
The invention relates to a method for determining or characterizing the coking tendency of baseoils and additive-treated oils.
2. Description of Background Materials
A number of standardized procedures exist for determining the coking tendencies of oils.
U.S. Pat. No. 3,248,327 discloses one test known as the Coker Detergency Test. This test is a modification of the Pratt and Whitney Test as described in United States Air Force Military Specification MIL-L-7808A. The test involves splashing the test oil in an air atmosphere against a heated aluminum panel for a given period of time and thereafter determining the amount of deposit formed on the panel. The oil is splashed onto the underside of an aluminum panel, and after a set period of time the test is stopped, and the aluminum panel is washed to remove excess non-coked oil. It is assumed that any increase in weight of the panel, after washing and drying, must be due to coke formation on the aluminum.
A similar technique is disclosed in U.S. Pat. Nos. 3,095,377 and 3,153,622, and is identified as a Panel Coker Test meeting United States Air Force specification MIL-L-9236A.
Yet another test is disclosed in U.S. Pat. Nos. 2,812,319 and 2,716,089, in which oil is heated and stirred in an aluminum measuring cup for a set period of time, after which the heated oil is permitted to settle without stirring. Thereafter the cycle is repeated a number of times, after which the oil is poured out of the cup, and the cup weighed to determine any increase in weight which would be indicative of coking.
Despite providing information as to the amount of coke which is formed, the above techniques are by their very definition imprecise and clumsy. These tests are subject to inconsistent results because of the numerous mechanical manipulations which are involved. Furthermore, none of the above techniques relies upon the measurement of asphaltenes as being an indicator of the coking tendencies of lubricating baseoils, but rather rely only upon the direct measurement of coke deposits.